Discovery of Bisulfite and an Uncharacterized Carbon-Centered Radical Systems in Non-Dry-Hopped and Dry-Hopped Beers Using a Different Spin Trap, 5, 5-Dimethyl-1-Pyrroline-N-Oxide, and a New Electron Paramagnetic Resonance Method

The amount of bisulfite (HSO3−, hydrated SO2) needed in beer to extend flavor stability is controversial with results that show elevated HSO3− levels in beer improves beer shelf-life analytically, yet decreases sensory flavor and flavor stability. Electron paramagnetic resonance (EPR) beer methods, using the N-tert-Butyl-α-phenylnitrone (PBN) spin trap, can detect the hydroxyl and ethoxy radicals from ethanol (•OH/CH3C•HOH). Water soluble 5, 5-Dimethyl-1-Pyrroline-N-Oxide (DMPO) trapped bisulfite (•SO3-) and uncharacterized C-centered radicals in vastly different dry-hopped (DH) and non-dry-hopped (NDH-a and NDH-b) beers and can also trap radicals of nitrogen and oxygen. A new DMPO capillary tube method detected •SO3- and C-centered radicals in cold stored and forced aged DH and NDH beers, dosed with 3 mM and 5 mM of sodium sulfite (Na2SO3), and displayed substantially higher •SO3- radical signals from the 5 mM versus 3 mM Na2SO3 dosage. The lowest SO2 DH beer had greater polyphenols (antioxidants) and significantly less •SO3- radical activity than the lower polyphenols NDH beers, indicating higher polyphenols in the DH beer quench more •SO3- and uncharacterized C-centered radicals by way of H2O2 reduction. Increasing polyphenols and reducing beer SO2 levels can potentially improve beer flavor stability and reduce bisulfite allergies in humans.